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The growth of crops, aquatic animals, and microorganisms living in water directly depends on the salinity of the water. Therefore, we need to use salinity meters regularly to check the water quality. In this article, Reecotech will provide you with the common methods of measuring water salinity currently available.
What is Salinity?
Salinity, also known as salt content, is denoted by the symbol S‰ (where S stands for Salinity). It is defined as the total amount of dissolved substances in 1 kilogram of water, measured in grams.
Salinity is commonly expressed in parts per thousand (ppt) or percent (%).
Salinity plays a crucial role in determining various aspects of the chemical composition of natural water and the biological processes occurring within it. Along with temperature and pressure, it acts as a thermodynamic state variable that influences the physical properties of water, such as density and heat capacity.
Why is it important to measure water salinity?
- Water salinity plays a crucial role in the growth and development of aquatic organisms, aquaculture species, and crops that depend on water salinity.
- Each type of aquatic organism or cultivated species has different adaptation abilities to different water salinity environments.
- Measuring and controlling this index is essential to ensure environmental standards for organisms and their growth and development.
- Water salinity also affects the concentration of dissolved oxygen in water. The higher the salinity, the lower the oxygen solubility, and vice versa. This affects the respiration, health, and survival of aquatic ecosystems.
- Salinity is also one of the critical factors in identifying and assessing climate change.
- Determining water salinity is a very important measurement, especially for seawater or estuaries where freshwater and saltwater meet.
Current Salinity Standards in Water
Here are some salinity assessment criteria that you can refer to:
- Freshwater: 0.01 – 0.5 ppt (rivers, lakes, reservoirs)
- Slightly Brackish Water: 0.01 – 0.2 ppt
- Slightly Saline Freshwater: 0.2 – 0.5 ppt
- Brackish Water: 0.5 – 30 ppt (lakes, inland seas, estuaries)
- Slightly Brackish Water: 0.5 – 4 ppt
- Moderately Brackish Water: 4 – 18 ppt
- Saline Brackish Water: 18 – 30 ppt
- Saltwater: above 30 ppt
- Seawater: 30 – 40 ppt (oceans, seas, inland seas, bays, estuaries)
- Hypersaline Water: 40 – 300 ppt (some lakes, bays, estuaries)
If the salinity of the water source is higher than the allowable level, appropriate and timely measures must be taken to ensure the quality of water for living and the environment for animals, plants, and aquatic animals to grow and develop.
4 Popular Methods for Measuring Salinity in Water
Measuring Salinity with a Hydrometer
Glass Hydrometer for Salinity Measurement
A glass hydrometer for salinity measurement is a tool used to determine the salinity of water. It consists of a cylindrical glass tube with a column of mercury or alcohol inside. When immersed in water, the mercury or alcohol column will rise to a certain level, corresponding to the salinity of the water.
The glass hydrometer for salinity measurement has a similar structure to a regular glass hydrometer, but it has a specific scale for measuring the salinity of water. The salinity scale of a glass hydrometer is usually divided in parts per thousand (ppt), with values from 0 ppt to 35 ppt.
To use the hydrometer, simply place it in the water to be tested and read the measurement result on the scale of the tube.
The lower the hydrometer sinks in the water, the lower the salinity, and vice versa.
Advantages: Easy to read results with high accuracy and compact size.
Disadvantages: Fragile, high cost.
Handheld Plastic Hydrometer
A handheld plastic hydrometer is a tool used to measure the salinity of water, commonly used in aquaculture. The user simply fills the hydrometer with the water to be tested and then places it on a flat surface. The needle inside will rise according to the salinity of the water.
Advantages: Low cost, easy to test salinity
Disadvantages: Large instrument size
=> Reference: Monitoring water quality and oceanography in aquaculture
Refractometry for Salinity Measurement
A refractometer is a device used to measure the salinity of water based on the principle of refractive index measurement. The refractive index is the deviation of light when passing through a different medium. Dissolved salts in water will increase its refractive index.
Components of a Salinity Refractometer:
- Prism: The prism is the most important part of the refractometer, and it functions to split light into two beams.
- Scale: The scale is divided in parts per thousand (ppt) units, with values ranging from 0 ppt to 35 ppt.
- Eyepiece: The eyepiece is used to observe the salinity scale divisions.
Advantages:
- Supports a wide measurement range
- Does not require energy like pi or electricity but uses direct sunlight
- High accuracy, durability, and long service life
- Supports automatic temperature compensation and manual or automatic calibration
- Simple and easy to use
Disadvantages: Higher cost compared to a hydromete
Using a Salinity Pen
If you are looking to use electronic devices instead of mechanical or optical devices, then a salinity pen is a device you might consider.
Features:
- Compact size
- High salinity range
- Direct display of results on LCD screen
- Salinity measurement range up to 70,000ppt
- Displays measurement units in ppt, PSU or specific gravity along with temperature
- Automatic temperature compensation (ATC)
- Manual or automatic calibration capability
Applications:
- Salinity testing of aquaculture ponds
- Salinity testing of seafood farms
Advantages:
- High accuracy salinity measurement
- Fast measurement time
- Supports multiple measurement units
Disadvantages:
- The device needs to be calibrated regularly
- The price is relatively high compared to the above devices.
Using a Digital Salinometer
Digital salinometers operate on the same principle as mechanical models, but with higher accuracy. In addition to measuring salinity, they also provide results in newer standard practical salinity units (PSU), PPT, and SG.
Simply insert a sample into the device and the salinity value will be displayed immediately. This measuring device is highly accurate.
Reeco Tech offers the following salinometers:
- EC300A handheld salinometer
Advantage:
- High precision
- Measure time quickly
- Supports many salinity measurement units
Salinity Sensor Probe – Salinity Meter
Salinity measurement in laboratories is often performed using a sensor probe in conjunction with various handheld salinity meters.
Reecotech offers a variety of salinity meters, including:
- YSI Pro1030 Salinity, Conductivity, pH and ORP Handheld Meter
- YSI Pro2030 Salinity, Dissolved Oxygen, Conductivity and Temperature Handheld Meter
- Online Salinity Meter
=> See more: Equipment to measure most water quality
Conclusion
The salinity of water has a direct impact on the development of crops, aquatic products, and microorganisms. Therefore, choosing the right salinity meter and regularly checking the salinity is very important. If you are in need of a salinity meter, please contact Reecotech immediately for advice and detailed quotation according to the information below.
REECO Science and Technology Company Limited
- Address: Room 202B, Building A, Software Park, Vo Truong Toan Street, National University of Ho Chi Minh City, Ward 6, Linh Trung Ward, Thu Duc City, Ho Chi Minh City, Vietnam
- Email: info@reecotech.com.vn
- Hotline: 0938 696 131 (Sales Department) / 0901 880 386 (Technical Service Department)
- Website: reecotech.com.vn
- Fanpage: Reeco Tech Co.,Ltd